The Potential of Ozonation to Reduce Impact of Waste Sludge-Entrapped Microplastics to Biogas Production

ABSTRACT

Due to low degradability of plastic materials, high usage, and low cost, microplastics (MPs) is becoming ubiquitous environmental pollutant. Wastewater treatment plants (WWTP) are one of main sources, where most of the MPs from wastewaters ends in waste sludge. Anaerobic digestion is one of most promised techniques of waste sludge management. The aim of this paper was to evaluate the impact of polyethylene terephthalate (PET) and polypropylene (PP) microplastics in the waste sludge with and without ozonation as possible pretreatment, on biogas and methane production with OxiTop® method. In the first set of experiments, PET inhibited (up to 6% at 0.1 g L⁻¹) or promoted (up to 3% at 1 g L⁻¹) methane production but increased cumulative biogas production (up to 38% at 0.5 g L⁻¹). PP inhibited methane production (up to 5% at 0.5 g L⁻¹) but its impact on biogas production was dependent upon concentration of MPs added. In the second set of experiments, pretreatment of non-contaminated waste sludge by ozonation (3.54 g_ozone h⁻¹) inhibited methane yield. Longer time of ozonation of PP-contaminated waste sludge reduced inhibition of methane yield, while in the case of PET-contaminated waste sludge, it was increased.

Graphical abstract

KEYWORDS:

• Biogas production
• methane yield
• ozonation
• polyethylene terephthalate
• polypropylene
• waste sludge

Acknowledgments

The authors are very grateful to Nina Kukovičič and Taja Černic for their laboratory assistance. Contribution and assistance of dr. Ula Rozman and assist. prof. dr. Marija Zupančič from Faculty of Chemistry and Chemical Technology, University of Ljubljana, are greatly acknowledged as well as the help with statistics of Dr. Igor Boševski.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author, upon reasonable request.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/01919512.2024.2332286.

Additional information

Funding

This research was funded by the Slovenian Research and Innovation Agency ARIS (Research Program Chemical Engineering P20191 and Research Program Mechanisms of Health Maintenance P30388 and Research Projects J2-4427, L7-4422). The authors acknowledge the support of the Centre for Research Infrastructure at the University of Ljubljana, Faculty of Chemistry and Chemical Technology, which is part of the Network of Research and Infrastructural Centres UL (MRIC UL) and is financially supported by the Slovenian Research and Innovation Agency ARIS [Infrastructure programme No. I0-0022].